1. Field of the Invention
The present invention relates to a thin-film magnetic head having a heating element for adjusting a flying height during write and read operations, a head gimbal assembly (HGA) provided with the thin-film magnetic head, and a magnetic disk drive apparatus provided with the HGA.
2. Description of the Related Art
In a magnetic disk drive apparatus, when writing or reading data signals, a thin-film magnetic head hydrodynamically flies with a predetermined spacing (flying height) on a rotating magnetic disk as a magnetic recording medium. While flying on the magnetic disk, the thin-film magnetic head writes data signals to the magnetic disk by applying signal magnetic fields with the use of an electromagnetic coil element, and reads data signals by sensing signal magnetic fields from the magnetic disk with the use of a magnetoresistive (MR) effect element.
With higher recording density due to the increase in data storage capacity and miniaturization of the magnetic disk drive apparatus in recent years, a track width of the thin-film magnetic head is becoming smaller. In order to avoid the degradation of writing and reading performances due to the smaller track width, latest magnetic disk drive apparatus actually has the flying height reduced down to the order of 10 nm or less.
The flying height, which shows such extremely small value, is required to be stably controlled, so as to avoid the thermal asperity and the crash and to maintain favorable read and write characteristics.
As a method for controlling the flying height, for example, U.S. Pat. No. 5,991,113 describes the developed technique for adjusting the flying height, in which a heater is provided within a thin-film magnetic head, and the ends of the electromagnetic coil element and the MR effect element are protruded toward the magnetic disk due to the heat generated from the heater.
In this technique, the effective protrusion of the element ends requires intensive heating of the intended region within the head. To meet the requirement, in Japanese patent Publication No. 2004-335069A, the sheet resistance of the heating portion of the heater is set to be larger than that of the lead portion, so that the amount of heat generated from the heater is set to be larger. Here, the sheet resistance is defined as a resistance ρ/d in the case that the current flows in the length direction of a square-shaped sheet conductor having the length and width equal to each other, the thickness d, and the resistivity (specific resistance) ρ. Further, Japanese patent Publication No. 2002-56952A discloses the technique, though for the ceramic heater for water heating, in which the sheet resistance of the electrodes is set to be smaller than that of the heating resistor to improve the heat exchange efficiency.
Further, it shows a significant effect of improving the protrusion efficiency of these element ends that a heater is provided between the electromagnetic coil element and the MR effect element to heat both elements from the neighborhood of both elements. In the case, two shield layers, which is provided so as to sandwich the MR effect multilayer as a magneto-sensitive portion of the MR effect element, especially act as the heatsink of the heater, and play a role of avoiding disadvantages due to excessive increase in temperature, such as the deformation or breaking of the heater itself. Generally, the shield layer is formed of a magnetic metal, and has larger heat conductivity compared to the surrounding insulating portions. Therefore, the shield layer is suitable for the heatsink of the heater.
Meanwhile, for the purpose of improving the ability for sensing magnetic field, Current-Perpendicular-to-Plane giant magnetoresistive (CPP-GMR) effect elements or tunnel magnetoresistive (TMR) effect elements are lately being used as the MR effect element. These elements have two shield layers, which sandwich the MR effect multilayer and also act as electrodes. The two shield layers further sandwich an insulating layer provided to prevent sense currents from being short-circuited, which causes some stray capacitance to be generated. Because the stray capacitance is likely to cause the noise in the read output of the MR effect element, the area of the two shield layers is recently set to be smaller so that the stray capacitance is decreased as much as possible.
However, smaller area of the shield layers is likely to cause a portion of the heater to run (extend) off the shield layers. The run-off portion has no heatsink, and thus, is likely to excessively increase in temperature by its own heat. As a result, in some cases, the run-off portion may suffer disadvantages such as deformation or breaking, which leads to the problem of the stability and reliability of the heater. Recently, the need for low power consumption of the apparatus requires the total resistance of the heater to be larger, which forces the current path of the heater to become longer. Therefore, it becomes seriously difficult to prevent a portion of the heater from running off the shield layers.
As might be expected, in the case that Current-In-Plane giant magnetoresistive (CIP-GMR) effect elements are used as the MR effect element, the same problem as described above may occur because a portion of the heater is likely to run off the shield layers, as the area of the shield layers is becoming smaller due to the requirement of the head miniaturization.